Adjust default config location on FreeBSD

[skillcoder]

Problem description
Current default linux config location (/etc/netbird/config.json) inappropriate for FreeBSD
On FreeBSD according to HIER(7) /etc/ using only for base system configuration files and scripts; see intro(5)
The standard /usr/local/etc/netbird/config.json is also not the best choice since this is an automatically generated config that we should never need to modify by hand, all changes to it making by up command. Therefore, I propose placing config into /var/db/netbird/, which is the standard location for system service state on FreeBSD.

To Reproduce
Just run current 0.28.7 client on FreeBSD without specifying --config/-c argument.

Expected behavior
Netbird state should store by default in the standard system service state location inside /var/db/netbird/

Are you using NetBird Cloud?

Yes

NetBird version

0.28.7

NetBird status -d output:

Related `netbird status -d' command output:

...
OS: freebsd/amd64
Daemon version: 0.28.7
CLI version: 0.28.7
...

Additional context

This is required to simplify usage netbird cli command on FreeBSD

[skillcoder]

I will prepare a PR

[mlsmaycon]

Thanks @skillcoder for the issue and for working on the PR.

[skillcoder]

Need to test after we release new version.